1. Technical Field
The present invention relates to an image processing apparatus for scanning an original image on a medium and obtaining image data to display the image, and more particularly to an image processing apparatus for determining whether the original image is a color image or monochrome image and obtains image data that has undergone image processing suitable for color if the original image is color or obtains image data that has undergone image processing suitable for monochrome if the original image is monochrome.
2. Related Art
It is well known that whereas tone reproduction is important for color images that typify photographs and halftone images, optical density contrast and edge sharpness are important for monochrome (typically black and white) images that typify character-based document images. On the other hand, there are some image forming apparatuses, such as a digital color copiers, that are provided with an auto color select (ACS) function to automatically determine whether the original image is a color image or a monochrome image and to automatically switch the type of image processing in accordance with the result of the determination. The ACS function is also called a color/monochrome auto-switching function.
The pre-scan system has been known a long time as an ACS system in color image forming apparatuses. In this system, by scanning the image of a document prior to an image forming operation, such as copying, the original image can be determined to be color or monochrome and a selection is made as to which image processing for color or monochrome is applicable in accordance with the result of the determination before an image forming operation is performed.
However, a problem in the pre-scan system is that the start of the image forming operation is delayed since a certain amount of time is required for the pre-scan. Thus, systems have been proposed for implementing the ACS function without pre-scan, such as Japanese Patent Laid-Open Publication No. 2001-285653 (referred to hereinafter as document 1) and Japanese Patent Laid-Open Publication No. 2000-261676 (referred to hereinafter as document 2).
In the apparatus given in document 1, the YMCK image data for color image formation and the K image data for black and white image formation are generated in parallel from the input RGB image data, for example, and are temporarily stored in the page memory. If the result of the ACS determination is color or black and white, the YMCK image data or the K image data for black and white image formation is retrieved from the respective page memory and used for image formation.
Document 2 also shows a system that scans an original in a scan mode with the largest amount of data (such as color mode) and subsequently converts the scanned data as needed to a data to accommodate the type of original (such as grayscale mode or binary monochrome mode).
The system of document 1 has a problem where a high capacity page memory (buffer) is required since the YMCK image data for color image formation and the K image data for black and white image formation are stored in the page memory.
The system of document 2 requires less page memory capacity than the system of document 1 since only the scanned data for the color mode is stored. However, in this system, if the original is black and white, the raw scanned data is not used. Instead, a monochrome image is generated from data of the color mode that has undergone image processing for color. Therefore, this has a problem where the resulting monochrome image has an image quality that differs from when image processing for monochrome is directly performed on the raw scanned data. Furthermore, the image processing for color that has already been performed may adversely affect the image quality of the image processed result when the monochrome image is generated.
The present invention provides, in an apparatus for performing ACS processing in parallel with image processing, a system that can execute processing with a relatively small buffer capacity and ensure the image quality of monochrome images.